U.S. Pat. Nos. 3,982,785 (Ambasz, Sep. 28, 1976) and 4,084,850 (Ambasz, Apr. 18, 1978) describe and show chairs in which the seat bottom slides forward from a resiliently restrained rearward position and the seat back tilts rearwardly from a resiliently restrained upright position, the seat and back movements being entirely independent and being produced automatically when the person sitting in the chair changes position from an upright posture to a reclining posture. The inventions of those patents have been very successfully commercialized as the well-known "Vertebra.RTM." seating made under license and sold in many parts of the world. The "Vertebra.RTM." line includes institutional and office models including four-legged unupholstered chairs with and without arms, tandem seating, lightly upholstered operational chairs, and more heavily upholstered managerial and executive desk and side chairs. All models have essentially the same seat frame based on parallel side tubes connected by a cross-piece, a seat bottom having sleeves on either side that are received telescopically and slidably on cantilevered front parts of the side tubes and a seat back connected to the upright back-supporting parts of the side tubes by resilient, articulated linkages. The "Vertebra.RTM." chairs are renowned especially for providing optimal body weight distribution and excellent sacro-lumbar support and for their ability to change position automatically according to the sitting posture assumed by the user.
When a person sitting in a "Vertebra.RTM." chair shifts between an upright posture and a somewhat reclined posture (leaning back) and the seat bottom slides forward or backward, the person's back has to slide up or down the seat back, which can cause pulling and rumpling of clothing and can at times be bothersome. Also, in the reclined position, the person's back is supported in a higher part than it is in an upright position, and the lumbar region is, therefore, not as well supported in the reclined position.